A method for determination of aluminum and phosphorus in biological materials, based on activation in a nuclear reactor and measurement of 28Al, produced by the 27Al(n, gamma)28Al and 31P(n, alpha)28Al reactions, is described. Irradiations in the undisturbed and epicadmium spectra provide a two-equation system in order to determine the contributions of aluminum and phosphorus to the total activities. Germanium is used as an integral flux monitor and comparator, through the reactions: 74Ge(n, gamma)75Ge, 76Ge(n, gamma)77Ge, and 72Ge(n,p)72Ga.